The present invention relates to gaskets which prevent leakage of radio frequency signals when mounting shielded radio electronics. Specifically, such gaskets can be used to achieve a safe connection between a shielding box and a printed circuit board (PCB) in devices such as radio telephones.
In order to prevent the leakage of radio frequency signals between components of radio electronics devices, a gasket must ensure good contact between the surfaces of the two mounted components. Adequate contact requires that the distance between contact points should be less than or approximately equal to a predetermined ratio (e.g., 1/20th) of the wavelength of the radio frequency to be shielded. As the radio frequency increases, the wavelength decreases. Therefore, effective shielding of high radio frequencies requires a shorter distance between adjacent contact points than low radio frequencies. Because the surface of one or both of the components can be rough or uneven, it is desirable that the gasket include flexible extensions such as spring arms which contact the adjacent component at finite contact points. A gasket having a flat or inflexible contact surface is likely to allow large or difficult to predict distances between contact points with an adjacent component surface.
One conventional gasket design 20 is shown in FIGS. 9 and 10. This gasket 20 includes a plurality of spring arms 22. Each spring arm 22 has one free end 24 which projects out of one side of a gasket body 26. A component which is mounted adjacent to that side of the gasket body 26 is, at minimum, contacted at areas separated by a contact distance D. Each spring arm 22 is stamped out of the gasket body 26, and therefore has a thickness T1 equivalent to a thickness T2 of the gasket body 26. As a result, if a low spring constant, and therefore thin spring arm 22 is desired, the gasket body 26 itself must be equally as thin. A disadvantage of this design is that the thinner the gasket body 26, the more difficult the gasket body 26 is to mount and assemble. A second disadvantage of this design is that the side of the gasket body 26 opposite the side from which spring arms 22 project presents a generally flat surface 28 to one of the components between which the gasket 20 is mounted. The flat surface 28 does not ensure known contact points with a component adjacent the flat surface 28. Absent known contact points, the shielding effect of the gasket 20 can be compromised if the component adjacent the flat surface 28 of the gasket has a rough or uneven surface, causing the gasket to have contact gaps greater in length than the wavelength of the radio frequency to be shielded.
FIGS. 11 and 12 show a conventional gasket 30 of similar construction to the gasket 20 shown in FIGS. 9 and 10. However, gasket 30 has spring arms 32 each having a thickness T3 smaller than the thickness T4 of the gasket body 34. This arrangement is achieved by etching the spring arm 32 into the metal material which forms the gasket 30. Nonetheless, this configuration still presents a flat surface 36 to one of two components between which the gasket 30 is mounted.
The conventional gasket 40 shown in FIGS. 13 and 14 attempts to solve the problem of indefinite contact points inherent in a flat gasket surface by alternating downwardly projecting spring arms 42 and upwardly projecting spring arms 44. However, this configuration requires that for a given length spring arm L, the distance between contact points D1 on a component surface is about twice the length L. This design makes it difficult to maintain both a long spring arm, which has a long travel or tolerance for roughness or unevenness in a component surface, and a minimum small distance between adjacent contact points on the component surface adjacent the gasket 40. In addition, this design requires two bending steps (one to form the upwardly projecting spring arms 44 and one to form the downwardly projecting the spring arms 42) to form the gasket 40, making such a gasket difficult to manufacture.
Accordingly, a need exists for a gasket that includes spring arms that project from opposite sides of a gasket body 26, while still providing at least one set of long spring arms having low spring constants and maintaining proportionally small distances between adjacent ends of each set of spring arms.